def is_prime(num):
    if num < 2:
        return False
    for i in range(2, int(num**0.5) + 1):
        if num % i == 0:
            return False
    return True

primes = []
for i in range(2, 21):
    if is_prime(i):
        primes.append(i)

for i in primes:
    print(f"这个数是素数：{i}")
